The present invention relates to a phase shifter for switching passing phase of a high-frequency signal with ON/OFF control of a switching element, and, in particular, to a phase shifter, in which a micro-machine switch is used as a switching element.
Recently, the possibility of use of micro-machine switches for switching elements used in phase shifter has been indicated. The micro-machine switches are finely machined switching elements. The micro-machine switches are featured in less loss, low cost and small electric power consumption as compared with other elements. This kind of micro-machine switch is disclosed in, for example, Japanese Patent Laid-Open No. 17300/1997.
FIG. 1 is a plan view showing a phase shifter making use of a micro-machine switch described in the above-mentioned Japanese Patent Publication. In addition, a wavelength of a high-frequency signal RF transmitting through a main line 201 is assumed to be xcex. The phase shifter shown in FIG. 1 is a low deadline type phase shifter. More specifically, the main line 201 connects thereto two stubs 202a, 202b, which are opened at tip ends thereof and spaced away xcex/4 from each other. Further, other stubs 203a, 203a wit tip ends opened are arranged to be spaced from the stubs 202a, 202b. A micro-machine switch 209a having a contact 215 is arranged between the stubs 202a, 202b. Also, a micro-machine switch 209b having a contact 215 is arranged between the stubs 202b, 203b. 
The micro-machine switches 209a, 209b are put in OFF position, only the stubs 202a, 202b are loaded on the main line 201. Meanwhile, when the micro-machine switches 209a, 209b are put in ON positions the stubs 203a, 203b are further loaded on the main line 201 through the contact 215 of the micro-machine switches 209a, 209b. Accordingly, the stubs loaded on the main line 201 can be changed in electric length by making ON/OFF control on the micro-machine switches 209a, 209b. 
Susceptance on a side of the stubs from the main line 201 varies depending upon the electric length of the stubs being loaded. Meanwhile, passing phase of the main line 201 varies in accordance with such susceptance. Accordingly, the high-frequency signal RF transmitting through the main line 201 can be switched over in passing phase by making ON/OFF control on the micro-machine switches 209a, 209b. 
With reference to FIGS. 2 and 3, an explanation will be given below to a constitution of and an operation of the micro-machine switch 209b shown in FIG. 1. FIG. 2 is a plan view showing the micro-machine switch 209b in enlarged scale. FIGS. 3(A) to (C) are cross sectional views of the micro-machine switch 209b, FIG. 3(A) being a cross sectional view taken along the line C-Cxe2x80x2 in FIG. 2. FIG. 3(B) being a cross sectional view taken along the line D-Dxe2x80x2 in FIG. 2, and FIG. 3(C) being a cross sectional view taken along the line E-Exe2x80x2 in FIG. 2.
The stubs 202b, 203b are formed on a substrate 210 in a manner to provide a slight gap therebetween. A lower electrode 211 is formed on the substrate 210 in a position spaced from the stubs 202b, 203b. Also, a post 212 is formed on the substrate 210 in a position on an extension of a line segment connecting the gap between the stubs 202b, 203b to the lower electrode 211.
A base portion of an arm 213 is fixed to a top surface of the post 212. The arm 213 extends from the top surface of the post 212 to a region above the gap between the stubs 202b, 203b through a region above the lower electrode 211. The arm 213 is formed from an insulating material. An upper electrode 214 is formed on an upper surface of the arm 213. The upper electrode 214 extends from a region above the post 212 to a region above the lower electrode 211. A contact 215 is formed on an underside of a tip end of the arm 213. The contact 215 is formed to extend from a region above an end of the stub 202b to bridge the gap to further extend to a region above an end of the stub 203b. 
Further, a control signal line 204 is connected to the lower electrode 211. A control signal is applied to the lower electrode 211 from the control signal line 204. The control signal serves to make ON/OFF control of the micro-machine switch 209b for switching of connection of the stubs 202b, 203b. 
It is assumed that voltage is applied to the lower electrode 211 as the control signal. In this case, if, for example, positive voltage is applied to the lower electrode 211, positive charges are generated on a surface of the lower electrode 211 and electrostatic induction causes negative charges to be generated on an underside of the upper electrode 214, which faces the lower electrode 211. As a result, attractive forces between the both electrodes cause the upper electrode 214 to be drawn toward the lower electrode 211. Thereby, the arm 213 bends and the contact 215 displace downward. And when the contact 215 comes into contact with both the stubs 202b, 203b, the stubs 202b, 203b connect to each other via the contact 215 in high-frequency fashion.
Meanwhile, when application of positive voltage on the lower electrode 211 is stopped, attractive forces disappear, so that restoring forces of the arm 213 returns the contact 215 to its original position. Thereby, there is produced an opened state between the stubs 202b, 203b. 
In addition, the micro-machine switch 209a shown in FIG. 1 is also constituted and operates in the same manner as the micro-machine switch 209b. 
The micro-machine switch 209b shown in FIG. 1 necessitates the post 212 and the arm 213 for supporting of the contact 215, in addition to the contact 215 for connecting/opening between the stubs 202b, 203b. Also, the lower electrode 211 and the upper electrode 214 are further needed to control displacement of the contact 215. Therefore, the micro-machine switch 209b is large and complex in three-dimensional structure. The same is the case with the micro-machine switch 209a. 
When such micro-machine swatches 209a, 209b are used in a phase shifter, there is caused a problem that arrangement of the micro-machine switches 209a, 209b requires a large area to lead to large-sizing of the entire phase shifter. Also, manufacture of the micro-machine switches 209a, 209b having a complex construction necessitates many processes, and so the manufacturing processes for phase shifters become complex.
Therefore, an object of the present invention is to miniaturize a phase shifter, which makes use of micro-machine switches as a switching element.
Another object of the present invention is to simplify the construction of a phase shifter, which makes use of micro-machine switches as a switching element.
A phase shifter according to the present invention switches passing phase of a high-frequency signal by means of ON/OFF control of micro-machine switches.
A micro-machine switch according to a first example of the present invention comprises first and second distributed constant lines arranged on a substrate to be spaced from each other, a first control signal line connected electrically to the first or second distributed constant line for application of a first control signal composed of a binary change in voltage. The micro-machine switch also comprises a cantilever, one end of which is fixed to one of the first and second distributed constant lines and the other end of which is formed to be capable of coming toward and away from the other of the first and second distributed constant lines, the cantilever comprising an electrically conductive member. The micro-machine switch further comprises a first insulating section formed in a region where the other of the first and second distributed constant lines faces the cantilever, and a second insulating section for keeping a voltage value of the first control signal together with the first insulating section.
The cantilever unites the function as a movable contact and the function as a support for the movable contact. Accordingly, the cantilever corresponds to the contact 215, the arm 213 and the post 212 of a conventional micro-machine switch in terms of function, and the former can be formed to be small as compared with the latter and is simpler than the latter.
Also, the first control signal is applied to the first or second distributed constant line to control an action of the cantilever, so that the lower electrode 211 and the upper electrode 214, which have been conventionally necessary, are made unnecessary. In this regard, the micro-machine switch can be made small in size and simple in construction.
On the other hand, it is essential in the invention to provide a first insulating section for capacitive coupling and a second insulating section for holding of control voltage. However, it is possible according to the present invention to make small-sized a phase shifter making use of the micro-machine switch and to simplify the phase shifter simple in construction.
Also, a phase shifter according to a second example of the present invention comprises a main line, through which a high-frequency signal is transmitted, and a first distributed constant line connected to the main line and opened at a tip end thereof. The phase shifter also comprises a second distributed constant line arranged to be spaced from the tip end of the first distributed constant line and opened at a tip end thereof. The phase shifter further comprises a cantilever, one end of which is fixed to one of the first and second distributed constant lines and the other end of which is formed to be capable of coming toward and away from the other of the first and second distributed constant lines, the cantilever comprising an electrically conductive member. The phase shifter further comprises a first control signal line connected electrically to the first or second distributed constant line and for applying of a first control signal composed of a binary change in voltage, a first insulating section formed in a region where the other of the first and second distributed constant lines faces the cantilever, and a second insulating section for keeping a voltage value of the first control signal together with the first insulating section.
A phase shifter according to a third example of the present invention comprises a main line, through which a high-frequency signal is transmitted, a first distributed constant line connected to the main fine and opened at a tip end thereof, and a grounding arranged to be spaced from the tip end of the first distributed constant line. The phase shifter also comprises a cantilever, one end of which is fixed to one of the first and second distributed constant lines and the other end of which is formed to be capable of coming toward and away from the other of the first and second distributed constant lines, the cantilever comprising an electrically conductive member. The phase shifter further comprises a first control signal line connected electrically to the first or second distributed constant line and for applying of a first control signal composed of a binary change in voltage, a first insulating section formed in a region where the other of the first and second distributed constant lines faces the cantilever, and a second insulating section for keeping a voltage value of the first control signal together with the first insulating section.
In accordance with the first to third examples, a low deadline type phase shifter can be constituted. In the case where a low deadline type phase shifter is to be constituted, the second insulating section is constituted by two capacitors formed midway the main line, and both the first and second distributed constant lines and the first control signal line are enabled to be connected electrically to the main line between the two capacitors.
Alternatively, the first control signal line may be connected electrically to the second distributed constant line, and the second insulating section may be constituted by the open end of the second distributed constant line.
A phase shifter according to a fourth example of the present invention includes a first distributed constant line with a cut part, two second distributed constant lines having different electric length, and a micro-machine switch for switching the second distributed constant lines, which short-circuits the cut part of the first distributed constant line to vary passing phase of a high-frequency signal. The micro-machine switch comprises cantilevers provided every second distributed constant line, one ends of the cantilevers being fixed to one of the first and second distributed constant lines and the other ends of the cantilevers being formed to be capable of coming toward and away from the other of the first and second distributed constant lines, the cantilevers comprising electrically conductive members. The micro-machine switch also comprises a second control signal line connected electrically to one of the second distributed constant lines for application of a second control signal composed of a binary change in voltage, and a third control signal line connected electrically to the other of the second distributed constant lines for application of a third control signal complementary to the second control signal. The micro-machine switch further comprises first insulating sections, respectively, formed in regions where the other of the first and second distributed constant lines faces the cantilevers, and a second insulating section for keeping a voltage value of the second and third control signals together with the first insulating sections. In the micro-machine switch, the second and third control signal lines constitute a first control signal line.
A phase shifter according to a fifth example of the present invention includes a first distributed constant line with a cut part two second distributed constant lines having different electric length, and a micro-machine switch for switching the second distributed constant lines, which short-circuit the cut part of the first distributed constant line to vary passing phase of a high-frequency signal. The micro-machine switch comprises cantilevers provided every second distributed constant line, one ends of the cantilevers being fixed to one of the first and second distributed constant lines and the other ends of the cantilevers being farmed to be capable of coming toward and away from the other of the first and second distributed constant lines, the cantilevers comprising electrically conductive members. The micro-machine switch also comprises a first control signal line connected electrically to the first distributed constant line for application of a first control signal composed of a binary change in voltage. The micro-machine switch further comprises first insulating sections, respectively, formed in regions where the other of the first and second distributed constant lines faces the cantilevers, and a second insulating section for keeping a voltage value of the first control signal together with the first insulating sections. In the micro-machine switch, constant voltages, respectively, equivalent to respective voltage values of two states of the first control signal are applied to the respective second distributed constant lines.
With the above-mentioned constitution, it is possible to constitute a switched-line type phase shifter. In these cases, the cantilevers, respectively, may be provided on both ends of the respective second distributed constant lines.
In the above-mentioned cases, a first constituent example of the first insulating section is an insulating film formed on at least one of an upper surface of the other of the first and second distributed constant lines and an underside of the cantilever. Thereby, the first insulating section can be simply constituted.
Also, the phase shifter described above may comprise a first high-frequency signal blocking unit connected to the first control signal line to block passage of the high-frequency signal.
In this case, a first constituent example of the first high-frequency signal blocking unit comprises a high-impedance line connected at one end thereof to that one of the first and second distributed constant lines, to which the first control signal line is connected electrically, and having an electric length of about one fourth as long as a wavelength of the high frequency signal and a greater characteristics impedance than those of the first and second distributed constant lines. The first constituent example comprises a low-impedance line connected at one end thereof to the other of the high-impedance line and opened at the other thereof, and having an electric length of about one fourth as long as the wavelength of the high-frequency signal and a smaller characteristics impedance than that of the high-impedance line. In this case, the first control signal line is connected to the other end of the high-impedance line.
A second constituent example of the first high-frequency signal blocking unit comprises a high-impedance line connected at one end thereof to that one of the first and second distributed constant lines, to which the first control signal line is connected electrically, and having an electric length of about one fourth as long as a wavelength of the high-frequency signal and a greater characteristics impedance than those of the first and second distributed constant lines. The second constituent example comprises a capacitor with one of electrodes connected to the other of the high-impedance line and the other of electrodes connected to a grounding. In this case, the first control signal line is connected to the other end of the high-impedance line.
A third constituent example of the first high-frequency signal blocking unit comprises an inductance element.
A fourth constituent example of the first high-frequency signal blocking unit comprises a resistor element having a sufficiently greater impedance than those of the first and second distributed constant lines. In this case, the resistor element may be insertion connected in series to the first control signal line. Alternatively, the resistor element may be connected at one end thereof to the first control signal line and opened at the other end thereof.
In this manner, leak of a high-frequency signal to the first control signal line can be prevented by providing the first high-frequency signal blocking unit on the first control signal line.
Also, the phase shifter described above may comprise a fourth control signal line connected electrically to that one of the first and second distributed constant lines, to which the first control signal line is not, connected electrically, and for charging and discharging electric charges generated by electrostatic induction.
In this manner, the electric charges generated by electrostatic induction is charged and discharged through the fourth control signal line whereby the micro-machine switch is made stable in switching action and increased in switching speed.
Also, the phase shifter described above may comprise a fourth control signal line connected electrically to that one of the first and second distributed constant lines, to which the first control signal line is not connected electrically, and for applying of constant voltage having a reverse polarity to that of to first control signal, and a third insulating section formed on that one of the first and second distributed constant lines, to which the fourth control signal line is connected electrically, and for keeping a voltage value of the constant voltage applied from the fourth control signal line together with the first insulating section.
In this manner, if a predetermined voltage is beforehand applied to that distributed constant line, to which the first control signal is not applied, the first control signal can be correspondingly made small in voltage level.
The phase shifter described above may comprise a second high-frequency signal blocking unit connected to the fourth control signal line to block passage of the high-frequency signal. In this case, a first constituent example of the second high-frequency signal blocking unit comprises a high-impedance line connected at one end thereof to that one of the first and second distributed constant lines, to which the first control signal line is not connected electrically, and having an electric length of about one fourth as long as a wavelength of the high-frequency signal and a greater characteristics impedance than those of the first and second distributed constant lines. The first constituent example also comprises a low-impedance line connected at one end thereof to the other end of the high-impedance line and opened at the other end thereof, and having an electric length of about one fourth as long as the wavelength of the high-frequency signal and a smaller characteristics impedance than that of the high-impedance line. In this case, the fourth control signal line is connected to the other end of the high-impedance line.
A second constituent example of the second high-frequency signal blocking unit comprises a high-impedance line connected at one end thereof to that one of the first and second distributed constant lines, to which the first control signal line is not connected electrically, and having an electric length of about one fourth as long as a wavelength of the high-frequency signal and a greater characteristics impedance than those of the first and second distributed constant lines. The second constituent example also comprises a capacitor with one of electrodes connected to the other of the high-impedance line and the other of electrodes connected to a grounding. In this case, the fourth control signal line is connected to the other end of the high-impedance line.
A third constituent example of the second high-frequency signal blocking unit comprises an inductance element.
A fourth constituent example of the second high-frequency signal blocking unit comprises a resistor element having a sufficiently greater impedance than those of the first and second distributed constant lines. In this case, the resistor element may be insertion connected in series to the fourth control signal line. Alternatively, the resistor element may be connected at one end thereof to the fourth control signal line and opened at the other end thereof.
Leak of a high-frequency signal to the fourth control signal line can be prevented by providing the second high-frequency signal blocking unit on the fourth control signal line as described above.
Also, the phase shifter described above comprises first and second high-impedance lines connected at one ends thereof to the first and second distributed constant lines, and having an electric length of about one fourth as long as a wavelength of the high-frequency signal and a greater characteristics impedance than those of the first and second distributed constant lines. The phase shifter also comprises a capacitor with one of electrodes connected to the other of the first high-impedance line and the other of electrodes connected to the other of the second high-impedance line. In this case, the first high-impedance line may be connected at the other end thereof to the first control signal line, and the second high-impedance line may be connected at the other end thereof to a grounding.
With this constitution, the first high-frequency signal blocking unit is constituted by the first high-impedance line, the capacitor and the grounding. Also, the second high-frequency signal blocking unit is constituted by connecting the second high-impedance line to the grounding.
A method of manufacturing a phase shifter, according to the present invention comprises a first step of forming on a substrate a portion of a main line, a first distributed constant line connected to the portion of the main line, a second distributed constant line, an end of which is spaced from an end of the first distributed constant line, and a control signal line connected to the portion of the main line. The method also comprises a second step of forming a sacrificing layer in a region extending from a gap between the first and second distributed constant lines to the end of the first or second distributed constant line. The method further comprises a third step of forming a first insulating film on that portion of the sacrificing layer, which faces the end of the first or second distributed constant line, and a second insulating film on both ends of the portion of the main line. The method further comprises a fourth step of forming a cantilever of metal on an area extending from that end of the second or first distributed constant line, on which the sacrificing layer is not formed, to the first insulating film on the sacrificing layer, and at the same time forming other portions of the main line on the second insulating film and the substrate; and a fifth step of removing the sacrificing layer.
Thereby, the micro-machine switch described above can be manufactured in a loss number of processes.